Organic Light Emitting Diode (OLED) display screen is considered as the next generation of flat panel display due to its advantages of self emission, being free of backlight, high contrast, small thickness, wide view angle, fast response, being suitable for flexible panel, wide operating temperature range, simple configuration and manufacturing processes, etc.
OLED display device comprises an emission unit disposed on a substrate, which comprises two electrodes and an organic electroluminescent material layer interposed therebetween. In the prior art, a transparent glass is generally used as the substrate. A refractive index of the glass is generally 1.4-1.5 and a refractive index of the organic electroluminescent material layer is 1.7-1.8. Upon a light emitted from the electroluminescent material transmitting through the glass and enters into air, most of the light is confined to the organic electroluminescent material layer due to a total reflection. Only 20% of the photons can be emitted from the OLED device, so the external quantum efficiency of the device is just up to 17%. The low light extraction efficiency and external quantum efficiency may result in the following problems of the device: low optical efficiency, high power consumption, high temperature of chip, short lift time, and so on.
In the prior art, there are various technologies for improving the light extraction efficiency of the OLED display screen, comprising micro lens technology, photon crystal technology, nanowire technology, scattering layer technology, microcavity resonance technology, and so on. The scattering layer technology has advantageous of low cost, less spectral shift, better improving the external quantum efficiency, so it attracts many attentions. In the scattering layer technology, one scattering layer is disposed on the substrate of the OLED display screen to increase the external quantum efficiency. The current scattering layer is a thin film embedded with scattering particles therein, in which the scattering particles may not be distributed uniformly and be overlapped with each other to form multiple layers in the thin film due to a limitation of the manufacturing processes. As a result, the wavelength and strength of the light emitted from the OLED device may be changed as the view angle of the users is changed, that is, the OLED device has a serious color shift, so that the display quality is poor.